In a conventional method for collecting a gaseous sample, the worker needs to collect a lot of samples at different sampling spots and different sampling time. These sampling spots and sampling time depend on the conditions of this experimental area. These conditions include the direction of wind, the position of the polluting area, and the experimental environment, etc. The sampling times may be any time in a whole day and then the worker must collect several samples in a sampling spot during 24 hours regardless of day or night. If the experimental area is very big, the number of the sampling spots will be increased and the frequency of sampling will be also increased. So, the worker must make much effort in this job. Therefore, it is tried by the applicant to deal with this problem encountered with the prior art.